As your code currently stands, showResult(this.value) is only going to use the value of the clicked select box. Each time you click one of the selects, it will only send its value to the javascrit function and ignore the rest. I assume you want the values from all three to be taken into account every time one of them is clicked.

You will need the values passed to your showResult function to include the values from all three - probably use onClick="getElementById('selectboxid').value for all three and concatenate them in some way that your getphoto.php page will be able to interpret.